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The Grand Tree of Life (was RE: Unified Cladistics)



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Betty Cunningham
>
> "Norton, Patrick" wrote:
> > Such a cladogram would require perfect knowledge, which we will never
> > have on any subject.  that all the information about all known I think
> > this is an unreachable goal, since the evidence upon which the
> characters
> > are derived (fossils) is constantly increasing.  , not perfectly
> > distributed among all researchers basedunderstand it, characters in a
> > cladogram
>
> is this possible perhaps with extant animals (if not fossil species) in
> some foreseeable future?
>
> -Betty

At the level of every species of modern animal (which still represent only a
fraction of the totality of living things): no, not unless every human on
the planet were drafted into describing the anatomy and physiology and DNA
of the animals around, and not without some astronomically vast improvements
in computational speed and complexity.

Remember that new species of *living* animals and plants are being found all
the time, and that detailed anatomical descriptions of many well known
species (much less poorly known species) have not been published!!  There
have only been a few thousand zoologists in the history of humanity, but
there are millions upon millions of species out there.

Furthermore, as the number of operational taxonomic units increase in a
study, the number of possible trees which could describe that matrix
increases at a double-factorial rate; at 3 taxa, 3 dichotomous trees; at 4
taxa, 15 trees; at 5, 105; at 6, 945; at 10, 39,459,425.  At "millions upon
millions upon millions", the number of possible trees would probably exceed
the number of atoms in the Universe.

Does that mean the studies we do are useless?  Not at all!

In all sciences we need to sample from a larger population (that is why
scientists have to take statistics classes).  Astronomers do not need to
look at every single star in the sky to develop models of stellar evolution;
sedimentologists don't have to test every grain of sand on the planet to
determine patterns of different flow regimes; physicists don't have to drop
objects of every sort of material imaginable to generate equations of
gravity.  By the same token, phylogenetic systemicists don't have to sample
every single species possible to generate hypotheses of phylogenetic
relationships.

Yes, bigger samples (i.e., more taxa and more characters) will hopefully
generate more accurate pictures of the Tree of Life, just as an H-R diagram
of star size vs. star luminosity is more effectively generated using
hundreds of stars rather than a dozen.

Hope this helps.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-314-7843